1. Field
This application relates generally to communications, and to an access scheme for ultra-wide band communication.
2. Background
In a wireless communication system multiple wireless devices may communicate with one another via signals having frequencies within a given radio frequency band. Here, provisions may be made to prevent transmissions from one device from interfering with transmissions from another device. For example, some systems employ media access control that allows only one device to use a given medium (e.g., a radio frequency band) at a time. One way of accomplishing this is to require that each device check the medium to determine whether another device is currently transmitting over the medium. If the medium is in use, the device will delay transmitting until a later time when the medium is not in use. Alternatively, some systems use a signaling technique such as spread spectrum that modifies transmitted signals to reduce the likelihood of transmissions from one device interfering with simultaneous transmissions of another device within the same frequency band.
Techniques such as these may be employed in a variety of wireless communication systems. An example of such a wireless communication system is an ultra-wide band system. Ultra-wide band technology may be used, for example, in personal area network (“PAN”) or body area network (“BAN”) applications.
At least one access scheme has been proposed for use in ultra-wide band systems. For example, IEEE 802.15.4a proposes a channel access scheme for achieving a low duty cycle in an ultra-wide band-based wireless PAN. This proposal specifies the use of a superframe structure that is defined by a central personal area network coordinator. The superframe structure begins with a beacon and contains a slotted contention access period (“CAP”) and a slotted contention free period (“CFP”). For the CAP, it is assumed that a random channel access scheme such as ALOHA or carrier sense multiple access (“CSMA”) is employed. The PAN coordinator assigns the CFP slots. A data frame in every slot starts with a preamble sequence for the receiver to achieve channel acquisition. An additional inactive portion of superframe may further reduce the duty cycle.
An access scheme in a wireless PAN or BAN may need to support a variety of applications including, for example, audio streaming, voice calls, file transfers, and sensor data transfers. However, these applications may have significantly different requirements in terms of one or more of data rate, latency, burstiness, and error tolerance. Consequently, an access scheme preferably provides sufficient flexibility to handle different data rates simultaneously and maintain different levels of duty cycle for these applications and/or other applications.